Distributed in-vitro blood analysis within a hospital is also known as point-of care, bedside or patient-side testing. In the hospital point-of-care measurement art a typical installation consists of an array of blood analysis instruments in multiple remote locations. Point-of-care in-vitro blood analysis instruments of the prior art perform measurements of blood chemical concentrations on discrete blood specimens. A very typical example might be a hospital consisting of numerous medical units containing patient beds. In such a measurement application blood analysis instrumentation is placed at or near-patient locations, i.e. at the point-of-care, such as in the unit or even at the patient bedside. Instruments are sometimes placed at fixed locations, other times they are portable. There are of course also blood analysis instruments within the hospital's centralized blood testing laboratory.
The value of point-of-care blood analysis is derived from the improved medical outcomes and operational convenience of fast turnaround time of results, as compared to the much longer turnaround time of results from a remote central laboratory. However such improved service to be economical cannot come at a cost per blood analysis much higher than the cost of the service from the laboratory. The cost per blood analysis (commonly referred to as cost per test) of a point-of-care measurement is given by the total equipment cost per test (daily capital depreciation and maintenance cost divided by the number of blood analyses or tests per day) plus the cost per test of disposable components or test consumables. However, since the testing frequency per patient location is low, no economies of scale can be realized so that the capital cost of bedside units must be kept low, if the point-of-care costs per analysis are to be maintained at or below the cost of testing in the lab. Despite this basic requirement, prior are point-of-care blood analysis systems are only available at high unit cost which most of the time renders the use of one unit per bedside completely uneconomical. To remedy this situation, prior art units are shared among numerous beds, creating an additional set of problems associated with the need for safe transportation and movement of expensive instrumentation within the hospital environment and constant monitoring and management of the equipment's availability. In the alternative, one expensive analyzer is placed in a laboratory site within the unit or in a satellite stat laboratory close to the unit and serves an entire medical unit's blood testing needs with the patient blood samples being transported to it. This reduces cost per test, because the capital cost for the expensive analyzer is divided over a large test volume, but the associated increase in turnaround time and decreased operational convenience significantly diminishes the point-of-care value proposition. Thus, there exists a need for low cost bedside units for point-of-care analysis.
Conventional point-of-care blood analysis instrumentation is always in the form of a complete or nearly complete analyzer. It is capable on its own to deliver an analysis result (for example a blood concentration value) rather than just a raw sensor output. Although the array of point-of-care instruments in a hospital-wide installation often communicates analysis results (blood concentration data) to a central, general-purpose computer, that computer is simply used for centralized collection and aggregation of analysis results and other patient relevant data, but not for sensory signal analysis. That is generally carried out in the conventional self-contained point-of-care analyzer instrumentation.
Point-of-care blood analyzers include devices for both quantitative and qualitative blood measurements and generally include complex and expensive hardware as well as all of the measurement software required for complete analysis. Thus, a complete analyzer is provided at each measurement location, which results in high operating cost for the conventional system even when the analyzer units are shared among numerous beds.
Prior-art blood analyzers, particularly those for quantitative blood analysis, consist of numerous electronic components. There are blood sensors connected to signal conditioning amplifiers and filters, then digitization circuits. Digital signals are transferred to microprocessor and memory units contained within the analyzer. The microprocessor accepts the sensor signals and uses the internal software to calculate concentration values, i.e. the final analysis result. In these self-contained analyzers of the prior art, microprocessors and their software also control the measurement process itself by controlling fluidic processes, the temperature of the measurement chamber and quality control processes. They also control a display that outputs the calculated concentration value contained within the analyzer memory. The microprocessor further controls the transmission of the analysis result, and possibly the measurement parameters to a other devices such as a central data station. The central data station can be a general-purpose computer, located for example in the central laboratory, or it may be at a port on a network such as the hospital information system or the laboratory information system.
In a typical hospital installation there are numerous point-of-care blood analyzer instruments connected to a central data station in which the point-of-care blood analysis data is aggregated. That data is consolidated with other point-of-care data from other devices in the hospital's laboratory information system. The centralized data is used for archiving purposes, for patient billing as well as for quality assurance.
In prior-art point-of-care blood analyzers, particularly in quantitative analyzers with laboratory grade accuracy, the sensors and related measurement hardware are complex and expensive. Some sensors cannot be re-used and are thus particularly expensive, or if they are re-usable, mast be washed between uses adding cost to the fluidics hardware described below. Moreover, the sensors' output is often not simply related to concentration and the relationship is not fixed over time. Thus, sensors can require frequent calibration. Sensors are used in a discrete sampling manner rather than in an in-line continuous measurement manner. To perform the required discrete sample acquisition step, as well as the necessary sensor calibration and washing steps and addition of other reagents if required the analyzer includes fluidic elements. The fluidics hardware consists of a measurement chamber containing sensors, orifices and conduits for introduction and movement of fluids, reagent reservoirs, waste chambers and the like. The fluids are actuated by often complex and costly electromechanical components such as pumps and valves. U.S. Pat. No. 4,734,184 describes a typical example of prior-art fluidics in a point-of-care sensor system with reusable sensors, while U.S. Pat. Nos. 4,342,964 and 5,096,669 describe fluidics for unit-use disposable devices. The blood analysis procedure typically also requires control of the measurement temperature and sometimes gas pressures. This and other related measurement hardware, particularly in optical measurement technology, can also be expensive. In total these various complicating elements of prior-art point-of-care blood analyzers add significant cost to each device. Even if much of the electronic hardware and software were to be stripped out of a defeaturized point-of-care analyzer of prior art design there would still be significant other remaining cost of sensors and measurement hardware contained within the device. Thus, there has heretofore been limited financial incentive to try to simplify electronic hardware and software.
What increases the cost of current point-of-care analysis even more is the use of numerous instruments at a typical bedside location in a hospital for monitoring the patient's status. These include biochemical measurement devices such as point-of-care blood analyzers and physical monitoring devices such as patient monitors. There may be numerous different types of in-vitro blood analyzers at each point-of-care location. For example, there may be an analyzer to measure glucose, another to measure blood gases and still others to measure blood coagulation, cardiac markers and so on. Each of these conventional devices is a self-contained analyzer. Thus an instrumented bedside is not only crowded but consists of significant and often duplicated hardware associated with significant capital cost.
Attempts to integrate technologies into simpler, more consolidated point-of-care tools have included the modular approach described below with respect to the Diametrics and Agilent instruments. A different approach has been to design completely new instruments combining the different measurement technologies. But such redesigns are expensive and add to the cost of the final device. In summary, integration of prior art point-of-care medical equipment has proven difficult and the resulting devices are still very complex and therefore expensive.
One concept intended to address this problem is the approach of providing modules or defeaturized medical instrumentation for connection to other instruments. For example, the concept was discussed in “Internat. Fed. Clinical Chem., Proceedings of the 17th International Symposium, Nice, France June 1998, eds. P. D'oruzio, N. Fogh-Andersen and L. Larsson, Omnipress, Madison, Wis. USA, 1998. pp3-15. A defeaturized blood-analysis device configured as a modular subsystem of a complete blood analyzer is described in U.S. Pat. No. 6,066,243 to Diametrics. Blood analysis devices that are modular components of a patient-monitoring system are marketed by Agilent Technologies. Though these prior-art defeaturized devices have less hardware than a self-contained analyzer, they still contain many of the components of a complete analyzer. The commercial blood-analysis modules of the prior art contain at least a micro-processor unit and software for calculation of a concentration value from raw sensor signals and for control of the measurement process, quality assurance testing and thermal control. Prior-art modules also still contain complex electromechanical subsystems for driving the analyzer's fluidics. Moreover, the defeaturized devices of the above-cited prior art are intended for incorporation into the housing of a parent instrument, together again forming a completely self-contained bedside in-vitro blood analyzer. That parent instrument in turn is a special-purpose device not a general-purpose device which could be used with many modules. Thus even these attempts at defeaturization of the measurement devices of the prior art thus far have required much costly, specialized hardware at each measurement location. Thus, mere still exists a need for a low cost bedside instrumentation alternative.
Clinical laboratory regulations require hospitals to perform intermittent verification of the integrity of their blood analyzers. Hospitals administrators have also developed quality control protocols for verification of the proper function of their blood analyzers at the point of care. It is well known in the art of quality control that quality systems should effectively expose non-conformance in those elements of the instrument that are most likely to give error during use. Traditional laboratory quality control protocols have included measurements with the analyzer of liquid samples of known concentration. In point-of-care systems and especially in systems employing unit-use diagnostic devices various components of the sensor signals (signal levels and drift rate, noise level) are used to indicate non-conforming performance of the sensor and fluidics. Also, manufacturers have provided electronic devices that have been designed for use in checking the integrity of the electronics, software and electromechanical subsystems of the analyzer. The prior art contains examples of different configurations of electronic testers that have been useful in controlling point-of-care analyzers. U.S. Pat. No. 5,124,661 for example discloses an electrical test head for connection to a blood analyzer. The electrical test head plugs into the analyzer's sensor card connector and simulates the electrical outputs of a sensor card. U.S. Pat. No. 5,781,024 describes an instrument performance verification system. This patent describes a portable analyzer for contacting to a sensor card, the analyzer containing measuring circuitry and electrical verification circuitry within the single portable housing. U.S. Pat. No. 5,829,950 also discloses an electrical integrity test circuit internal to the instrument.
Another disadvantage of conventional distributed self-contained point-of-care devices resides in the quality assurance problem they present. Because they are self-contained analyzers they incorporate a fall suite of software to manage all aspects of the blood analysis. It is often the case that manufacturers issue new versions of software to update an analyzer to a new revision. This might be to enable new blood tests, or to provide better measurement algorithms to obtain more accurate results or to provide for correction factors if the calibration of manufactured batches of sensors or reagents have changed. A hospital installation that might comprise numerous (sometimes hundreds) such analyzers, each with its own software, can become a serious quality assurance problem in this kind of environment. This problem is compounded by the fact that at each point of care there may be analyzers from several manufacturers using very different measurement technologies, each analyzer having a full suite of software with several versions coexisting at one time. The professionals responsible for quality assurance of distributed instrumentation software in a chaotic environment such as a hospital recognize this to be a significant problem.
There remains a significant need in the field of healthcare to provide an improved point-of-care blood measurement system, that is both cost-effective and addresses problems of quality assurance in remote testing. The devices of the present invention address that need.
Distributed sensors for the production of sensory data are not used in the hospital environment. Although distributed sensors are known in an industrial setting, also known as all enterprise measurement system, they are not part of a smart card/card reader/general purpose computer combination. In contrast, in the industrial measurement art a typical installation consists of an array of sensors installed at multiple remote locations and connected to a central computer for data acquisition. A very typical example might be a chemical plant in which chemical processes occur in reactors connected by pipes. In such a typical measurement application, the factory engineers have found it necessary to measure quantities such as temperature, flow rate, acidity and dissolved oxygen at numerous different locations within the chemical plant. The engineers have installed these sensors in the various remote locations within pipes and reaction vessels. Electrical signals from sensors of this prior art are typically low-level outputs in the milli-volt range at high impedance from voltage generating sensors or micro-amp currents from current generating sensors. As such they are prone to pick up noise during transmission. Thus, each sensor is connected to a signal-conditioning device placed in close proximity to the sensor. The signal-conditioning device converts the raw electrical output from the sensor to a more robust signal that can be transmitted from the sensing location. Such a signal-conditioning device might be simply analog signal amplification and noise filtering circuitry when it is appropriate to transmit an analog level. Interposed between the central computer and the remote sensors and signal-conditioning device is a data acquisition interface. This device contains signal conversion circuitry and digital and/or analog input/output (I/O) circuits. The signal conversion circuitry digitizes the analog sensor signal and converts it into one of several digital data stream formats. Conditioned analog sensor signals can be converted by a data acquisition interface installed in the computer when the distance between remote sensors and computer is short. Such a device is called a data acquisition (DAQ) card. For long distances it is appropriate to install the data acquisition interface with signal conversion structure close to the sensor site. Such a conversion device might then digitize the sensor signal and convert it to one of several data stream transmission protocols such as RS232. As is known in the art it is also now feasible to transmit the data stream from the remote sensor to the central computer by either a wire connection or by radio waves over a wireless connection.
In the industrial measurement applications sensors generally deliver signals that are directly related to the concentration value through a fixed calibration factor. The calibration factor is constant over numerous measurements. The sensors thus do not need calibration at each use occasion. There is no requirement to wash and otherwise prepare the sensor for a new measurement. Sensors are used in a continuous in-line measurement situation rather than a discrete sampling application. Sensors in a continuous-monitoring biomedical application also resemble the above characteristics of industrial sensors. Manufacturers have developed general-purpose measurement and control devices to cost-effectively serve this industrial sensor market application. Thus devices such as general-purpose signal conditioning modules are available as articles of commerce. Data acquisition interfaces such as general-purpose DAQ cards, and I/O devices with RS232 transmitters or with radio frequency links are now all available as articles of commerce. The use of such general-purpose devices is well established in the prior art of industrial sensing. W.O. Pat. Nos. 9837804 and 0021434 disclose a modular measurement device for biomedical continuous monitoring sensors. These patents disclose an integrated element for connection to a general-purpose computer consisting of a DAQ PC card containing a sensor.